87 research outputs found
Sparse geometric graphs with small dilation
Given a set S of n points in R^D, and an integer k such that 0 <= k < n, we
show that a geometric graph with vertex set S, at most n - 1 + k edges, maximum
degree five, and dilation O(n / (k+1)) can be computed in time O(n log n). For
any k, we also construct planar n-point sets for which any geometric graph with
n-1+k edges has dilation Omega(n/(k+1)); a slightly weaker statement holds if
the points of S are required to be in convex position
Spanner Approximations in Practice
A multiplicative -spanner is a subgraph of with the
same vertices and fewer edges that preserves distances up to the factor
, i.e., for all vertices , .
While many algorithms have been developed to find good spanners in terms of
approximation guarantees, no experimental studies comparing different
approaches exist. We implemented a rich selection of those algorithms and
evaluate them on a variety of instances regarding, e.g., their running time,
sparseness, lightness, and effective stretch
Lower bounds on the dilation of plane spanners
(I) We exhibit a set of 23 points in the plane that has dilation at least
, improving the previously best lower bound of for the
worst-case dilation of plane spanners.
(II) For every integer , there exists an -element point set
such that the degree 3 dilation of denoted by in the domain of plane geometric spanners. In the
same domain, we show that for every integer , there exists a an
-element point set such that the degree 4 dilation of denoted by
The
previous best lower bound of holds for any degree.
(III) For every integer , there exists an -element point set
such that the stretch factor of the greedy triangulation of is at least
.Comment: Revised definitions in the introduction; 23 pages, 15 figures; 2
table
Spanner Approximations in Practice
A multiplicative ?-spanner H is a subgraph of G = (V,E) with the same vertices and fewer edges that preserves distances up to the factor ?, i.e., d_H(u,v) ? ?? d_G(u,v) for all vertices u, v. While many algorithms have been developed to find good spanners in terms of approximation guarantees, no experimental studies comparing different approaches exist. We implemented a rich selection of those algorithms and evaluate them on a variety of instances regarding, e.g., their running time, sparseness, lightness, and effective stretch
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